1. Industrial useful field
This invention relates to an improvement in a planetary gear train which constitutes, for example, an automatic transmission for automobile in combination with a four-element torque converter.
2. Prior art and its problem
A conventional Simpson's planetary gear train of this type is constructed as illustrated in FIG. 2.
The planetary gear, in FIG. 2, includes a pair of divided-one-another planetary gear assemblies 10 & 12 comprising planetary gears, planetary carriers, sun gears and ring gears disposed at a rear stage of a three-element torque converter consisting of a stator, a turbine and a pump; two sun gears 14 & 16 connected together; a planetary carrier 18 connected to ring gear 20; and an output from planetary carrier 18.
Brakes B1 & B2 and clutches C1 & C2 for controlling such gears are arranged in such Simpson gear train, and the brakes together with the clutches work as tabulated "O" in the following Table 1 to carry out a speed change of three forward speeds and one reverse speed.
TABLE 1 ______________________________________ (Prior Art) Brake & clutch C1 C2 B1 B2 ______________________________________ 1st -- O -- O 2nd -- O O -- 3rd O O -- -- Rev O -- -- O ______________________________________
A stage number of speed change has recently been multiplied from three forward speeds to four forward speeds in order to improve a performance of tractive force.
In the foregoing Simpson's planetary gear train, however, the speed change of three forward speeds and one reverse speed is used and a speed change of four forward speeds and one reverse speed becomes complicated in structure and is unsuitable for practical application.
Further, a conventional general Ravineaux's planetary gear train is constructed as illustrated in FIG. 3 and includes a planetary gear 110 which is comparatively long in its axial direction and meshes with a sun gear 116 and a ring gear 120 to form a single row planetary gear. Moreover, the planetary gear 110 is carried by a planetary carrier 114, a planetary gear 112 is carried by the planetary carrier 114 while meshing with the planetary gear 110, and the planetary gear 112 meshes with a sun gear 118 to form a double row planetary gear. Furthermore, a ring gear 120 meshing with an outer periphery of the planetary gear 110 is connected to an output gear 122.
Brakes B1 & B2 and clutches C1, C2 & C3 for controlling these gears are arranged therein, and the brakes together with the clutches work, as tabulated "O" in the following Table 2 to carry out a speed change of four forward speeds and one reverse speed.
For a speed change of three forward speeds, the clutch C3 is omitted.
TABLE 2 ______________________________________ (Prior Art) Brake & clutch C1 C2 C3 B1 B2 ______________________________________ 1st -- O -- -- O 2nd -- O -- O -- 3rd O O -- -- -- 4th -- -- O O -- Rev O -- -- -- O ______________________________________
A stage number of speed change has recently been multiplied from four forward speeds to five forward speeds in order for improving performance of tractive force.
In the conventional planetary gear train, however, the number of clutches will increase with an increase in a stage number of speed changes, and the structure and control become complicated.